Thermostatic device



J. H. DERBY THERMOSTATIC DEVICE Filed June 25, 1932 Jan. 29, 1935.

\;li//l/lllilil ,2 lummm if v w 22 W "W INVENTOR Jamv f1. DERBY Patented Jan. 29, 1935 UNITED STATES PATENT OFFICE 6 Claim.

This invention relates to-a thermostatic circuitclosing device, and particularly to such a device in which spaced circuit terminals are adapted to be electrically connected by a fusible conductor which is normally maintained under resilient pressure and which, when fused, is adapted to be forced by said pressure into circuit-closing contact between said terminals.

Thermostatic circuit-closing control devices of the type to which the present invention relates have been used prior to this invention, and one such device is described and claimed, for exampie, in my prior Patent No. 1,868,136. In fire prevention work, however, there is always a con- 23 stant and insistent demand for more rapid operation without any possibility that the device may fail to operate when the given temperature has been reached. It is an object of the present invention, therefore, to provide a device of the type described which will operate with absolute certainty, and which will operate more rapidly than any fusible metal type thermostat heretofore known, and which will be free from the possibility of operation under conditions other than 2.1 those for which it is designed to operate.

With these and other objects in view, my invention contemplates a. circuit-closing device .of the type specified, in which resilient circuit-terminal disks are secured together and insulated so from one another in such a way that they are resiliently pressed toward one another, and are held apart by an insulating disk bearing against a fusible connector. Advantageously, the circuit terminals are made of relatively thin resilient sheet metal and are dished inwardly so that the expansion of the metal, when heated, will increase the pressure between them, and thus will cause more rapid operation without increasing the normal pressure.

It has been found that several of the features specified above can be used independently of one another. Nevertheless, all contribute to produce a thermostatic device'which is capable of operating more rapidly and with certainty, and with greater freedom from deterioration over long periods of time than any which has heretofore been made.

In the accompanying drawing I have illustrated a preferred embodiment of my invention, and one modification thereof. These are given only by way of example, in order to assist in the exposition of the invention, and are not to be taken as limiting in any way the scope of the invention.

Fig. 1 is an axial section through a device embodying my invention;

Fig. 2 is atop plan view of the same; and

Fig. 3 is an axial section similar to that shown in Fig. '1, showing a modified form of the invention.

Referring to the drawing, the reference character 10 designates the exposed circuit terminal 5 made in disk form with a peripheral portion 11 turned up and over the insulating rings 12 and 13, so as to clamp these rings together and over the peripheral edge of the upper circuit terminal disk 14. A central portion 15 of the disk 10 is shaped to form a well in which is mounted a fusible metal disk 16 between the well 15 and the periphery. The disks 10 and 14 are dished inwardly as shown in, Fig. 1, so that thermal expansion of the metal will tend to drive the portions 15 and 18 more strongly toward one another.

Between the terminal disk 14 and the fusible disk 16, an insulating ring 17 is provided. This ring 17 is advantageously of a molded or accurately machined insulation such as phenol formaldehyde plastic, or other hardened synthetic resin plastic. This ring advantageously is held in place by means of a projection 18 formed in or secured to the center of the disk 14 which fits into a central opening in the insulating ring or disk 1'7. Normally this projection 18 serves also as the contact portion of the terminal disk 14,- that is to say, when the fusible material 16 is fused, it will flow into the central opening of the disk 17, and there will contact with the central protection 18 on the disk 14.

As has already been indicated above, the disk 10, or at least its central portion 15, is advantageously made of a thin resilient sheet metal e. g. a phosphor bronze, or a nickel alloy known as Monel metal.

In a preferred embodiment of the invention, the overall diameter of the disk 10 may be about 1% inches, the thickness of the disk 10 from 0.010 to 0.0125 inches, and the bottom of the portion 15 about 0.010 inches above the plane of the bottom of the disk at the peripheral edges beneath the ring 12. The distance between the fusible disk 16 and the projection 18 may be, for example, 0.015 inches to 0.030 inches.

In Fig. 3 I have illustrated a modified form of the invention in which the bottom of the disk 1'7, instead of being flat, is inwardly beveled or countersunk for the purpose of gathering the fusible metal toward the central opening of the insulating ring. The bevel in this case is shown somewhat exaggerated for the purpose of illustration, but in actual practice need be very slight.

Although I have described above a preferred 55 embodiment of my invention and one modification thereof, it is to be understood, nevertheless, that numerous other changes can be made without departing from the scope of this invention.

What I claim is:

1. A thermostatic circuit-closing device which comprises a pair of resilient sheet metal circuit terminal disks, one of said terminals being inwardly dished and having a well on its inner side near the center thereof, adisk of fusible metal in said well adapted at the operating temperature to flow into circuit-closing contact with both said circuit terminals, said fusible disk be-. ing in contact over substantially its entire area with said exposed terminal disk, a substantially rigid annular insulating disk securedto the other terminal disk between said circuit terminals,

having clean-cut, smooth faces and edges, 'and' peripheral insulation separating the terminal disks at the periphery, and spacing them accurately, said terminal disks being secured together at the periphery in slightly distorted condition whereby a desired resilient pressure will be exerted by said terminal disks upon the fusible and insulating disks.

2. A thermostatic device as defined in claim 1, inwhich the central insulating disk is dished on its surface toward the fusible disk, whereby to drive the fused metal toward the central opening through said insulation and into circuitclosing contact between the terminal disks.

3. A thermostatic circuit-closing device which comprises a pair of circuit terminal disks, the lower of which has a well thereon, a disk of fusi ble conducting material mounted within said well, and a substantially rigid plunger of insulationfitted to, but having clearance from the inside of said well and having smooth, clean-cut faces and edges, its lower. face presenting a contact area to the fusible material sufficient to support the pressure thereon, and positively secured against lateral movement in position between the fusible disk and the opposite circuit terminal disk, with its edges spaced from the sides of said well, said terminal disks being secured together so as to exert a resilient pressure upon the fusible material and central insulating disk.

4. A thermostatic circuit-closing device comprising a pair of circuit terminal disks, both made of stiff sheet metal shaped to effect buckling of the center upon thermal expansion, and positioned relative to each other so that the buckling .of each will be toward and opposed by the buckled part of the other, a well formed centrally upon one of said terminal disks and facing the other, and having sides approximately parallel to the direction of motion due to buckling, a fusible conductor in said well and in electrically conducting relation to said terminal disk; and an insulating plunger closely fitting to, but having substantial clearance from the sides of the well, held in position to maintain clearance, pressed against the fusible conductor by the terminal disks and having an opening through the central portion thereof through which the fusible conductor, when fused, may pass into electrically conducting relation to the other terminal disk.

' 5; A thermostatic circuit-closing device comprising a pair of circuit terminal disks, both made 7 of stiff sheet metal shaped to effect buckling of thecenter upon thermal expansion and positioned relative to each other so that the buckling of each will be toward and opposed by the buckled part of the other, a well formed centrally upon one of said terminal disks and facing the other, and having sides approximately parallel to the direction of motion due to buckling, a fusible conductor in'said well and in electrically conducting relation to. said terminal disk and a projection formed centrally upon the other terminal disk, and an insulating plunger closely fitting to, but held in position to maintain clearance from the sides of the well by said electrically conducting projection and having an opening therethrough into which the said projection extends and through which the fusible conductor, when fused, may pass to said projection, the projection serving to reduce the gap across which the fusible conductor must flow to close a circuit therethrough.

6. A thermostatic circuit-closing device comprising a pair of circuit terminal disks, at least one of which is made of stiif sheet metal shaped to effect buckling of the center upon thermal expansion, and the other adapted and positioned relative thereto soas to oppose said buckling, a fusible conductor positioned between said disks within the area of said buckling and in electrically conducting relation to one, and insulation between said fusible conductor and the other terminal disk'adapted to prevent electrical conduction therebetween under normal conditions, but to permit the fusible conductor, when fused, to pass it into electrically conducting relation to the other terminal disk.

JOHN H. DERBY. 

